A Celestial Spirit that is one of the 12 Golden Zodiac Keys. Her key is owned by Lucy Heartphilia. She is very powerful and does not get along well with Lucy to an extent that she would kill her.
Aquarius' Gate Key.
Aquarius is one of the 12 zodiac Celestial Spirits whose key is currently owned by Lucy. Its unknown when or where Lucy gained Aquarius' gate key since Lucy had been her master from the beginning of the series. However what is known, albeit a small tidbit, about Aquarius' history is that she was previously owned by Lucy's mother, Layla. When Layla retired from her work as a mage, she entrusted Aquarius' key to another mage and gave him or her proper instructions to present it to Lucy should she ever decide to become a Celestial Spirit mage.
Original Concept of Aquarius.
Aquarius, who was created by Hiro Mashima, was designed to have her appearance correspond with her respective zodiac sign whereby "Aquarius" is depicted as a merman or mermaid carrying a vessel from which is pouring a stream of water as reflected by the urn and water magic Aquarius uses in the Fairy Tail series. Her name is also Latin for "water bearer". In addition, her upper-body appearance is the same as Undine, the queen of water people, in Fairy Tale, a one-shot made by Mashima before Fairy Tail.
She made her first appearance in Chapter 1 of the manga and Episode 1 of the anime. She is voiced by Eri Kitamura in the Japanese version and Jessica Cavanagh in the English version.
Aquarius and Lucy aren't the best of friends.
One of the most important distinctions between Aquarius and the other Celestial Spirits is that while the other spirits serve Lucy obediently, Aquarius hates her with a fiery passion. Whenever she is summoned out she still attacks, but instead of attacking the opponent she attacks Lucy, but luckily her tidal wave attack is so large it usually sweeps up the opponent as well. So the risk of summoning her is great, because Lucy has said several times she is her most powerful Celestial Spirit. After her attack she then tells Lucy to not summon her for a certain amount of time, like a week or two, and then says she's going to go spend time with her boyfriend who is later revealed to be the Celestial Spirit Scorpio.
Lucy: Is this really Aquarius?!!
In contrast to her hostile and intimating attitude towards Lucy and even Cana,
Aquarius is sweet, kind and lovable towards Scorpio which is a
completely different side of herself. She even threatens Lucy to keep quiet about her moodiness in front of Scorpio unless she wants to be a "drowned corpse". But over the course of the series Aquarius has helped Lucy out several times despite her hatred for her. She was even the first Celestial Spirit she summoned out in the series.
Major Story Arcs
Aquarius when she was first summoned by Lucy.
As Natsu and Lucy fight Bora, the latter summons Aquarius and orders her to send Bora's ship full of captured girls to the harbor. Happy immediately takes a liking to her since she is a fish but Aquarius ignores this. However, she does turn to Lucy and threatens to kill her if she ever drops her keys again prompting a quick apology from the mage. After Aquarius washes the ship ashore, along with Lucy and Happy, she states her desire not to be bothered for a week since her boyfriend is taking her on vacation. Before she leaves, she rubs it in to Lucy's face that she has a boyfriend while Lucy doesn't.
Galuna Island Arc
Aquarius under Sherry's control.
Lucy re-summons Aquarius to deal with Sherry and her doll magic. But after realizing that Aquarius was a strong spirit, Sherry decides to use her magic to gain control of her. However her plan backfires as Aquarius' tidal wave attack engulfs both her and Lucy. Before leaving she berates Lucy's personality claiming that its the reason why she'll never get a boyfriend like she has.
Phantom Lord Arc
Lucy: Have mercy!
Although Aquarius doesn't make an appearance in this arc, Lucy does tell Mirajane that she received a very harsh punishment (spanking) from Aquarius for losing her keys when she got captured by members of Element 4.
Tower of Heaven Arc
Even Juvia's afraid of Aquarius.
Lucy summons Aquarius in her match against Vidaldus and Juvia, who was under his control. When Juvia liquefied herself, Lucy took advantage of the situation and summoned Aquarius through Juvia's water. Aquarius then attacked everyone in the room and Juvia and Lucy joined hands to cast Unison Raid, an extremely rare magic. Once the water receded and the two celebrated their victory, Aquarius mouths off at Lucy telling her never to summon her from a strange place again or else she'll kill her. She then wonders if she'll summon her next from inside a toilet bowl. She leaves again saying not to summon her for the next two weeks and commenting that Lucy should get a boyfriend.
Oracion Seis Arc
Aquarius reunites with her boyfriend.
Lucy summons Aquarius as her strongest Celestial Spirit in her fight against Angel. Desperate to defeat her opponent, Lucy tells Aquarius that she can do whatever she pleases so long as she defeats Angel. Aquarius agrees but is removed from the battle when Scorpio, her boyfriend, is summoned which is something that Angel was aware of but Lucy wasn't. The two then set off for their date with Angel's consent and to Lucy's dismay, forcing the latter to summon her trump card, Loke.
After Lucy and Natsu experienced a hellish coaster ride and landed in a pond courtesy of Hughes, Lucy summons Aquarius to fight the man. Unlike her usual self, Aquarius withholds her fight with her master and makes a move to attack her opponent. But to her shock, she realizes and then exclaims that she can't control the water because of Hughes ability to control everything in the park. This is one of the few times that her attack fails and gets thrown back at her.
S-Class Trial Arc
Aquarius' new victim: Cana.
While fighting Bixlow and Fried in the S-Class exam, Lucy uses the water from Cana's card to summon Aquarius. She angrily wave slashes everyone and comments how Lucy and Cana's use of bathing suits to distract man is a new low. However, Aquarius directs her hostility to Cana with whom she bickers stating that all women are her enemies because being "plump" does not equate to "justice". In the end, she gives Cana a zero as a woman while Cana calls her a cheap woman, showing that the two are similar in some way.
Powers & Abilities
Aquarius' water attack.
Much like her name suggests, Aquarius' magic deals with water which she absorbs in her urn and hurls with a tremendous force that is so strong that she can throw a yacht several hundred miles out at sea back to shore. But unlike her other Celestial Spirits, Lucy needs water
in order to summon her. This can be anything from a large ocean to a
small pot full of it, but once she even used Juvia's body in its water form to accomplish it.